QS Study

Atrioventricular (AV) Nodal Delay

Definition: Delay of impulse conduction from the atria to the ventricle is called Atrioventricular (AV) nodal delay. An important advantage of the AV node’s delay is that it normally prevents atrial fibrillation from escalating into ventricular fibrillation. It also confines the heart rate to around 150; if a pacemaker indication retriggers the AV node before the AV node’s delay was over, the early second trigger is discarded so the ventricle sees only one signal.

Duration: 0.09 sec.


  1. A smaller size of the AV nodal fibers than atrial fibers.
  2. The diminished number of gap junction between the fibers.
  3. Resting membrane potentials of these fibers are much negative than the normal resting membrane potential of cardiac muscle.
  4. AV nodal fibers ha low RPM thus fast Na+ channel remain blocked.
  5. Prolonged refractory period of AV node.
  6. Embryogenic.
  7. Very few gap junctions connect the successive fibers in the pathway so that there is great resistance to the conduction of excitatory ions from one fiber to the next.

Importance: It ensures completes atrial contraction before the ventricular contraction begins. For this delay, the atria get time to empty their content (blood) into the ventricles before ventricular contraction begins. This allows time for the atria to empty their blood into the ventricles and ensure the proper and diastolic volume of the ventricle.

Time from atria to ventricle –

SA → AV → 0.03 sec

In AV node → 0.09 sec

In AV bundle → 0.04 sec

Total delay → 0.16 sec.

So atria contract 0.16 sec before ventricle.